Veggie but sometimes fancy meat?

i'm veggie because i dont think its right how we differentiate between animals, using some for food and others for pets. however i occasionaly eat tuna, eating fish doesn't feel so bad to me. sometimes though i am drawn to eating beef, like a steak, although i haven't given in yet. is this my body telling me i need it for health reasons? is it my natural instinct? is being veggie just rules i've created in my mind which go against my bodily instincts from thousands of years?